A bending machine for the production of sheet-metal articles

Abstract: A bending machine comprises a fixed base (280), a cradle (282) mounted on the base (280) for pivoting about a horizontal pivot axis, and a tool-holder structure (288) carrying a punch (84) and a die (86) which cooperate with each other and define a bending line (292). The tool-holder structure (288) is rotatable relative to the cradle (282) about an axis of rotation perpendicular to the horizontal pivot axis and coinciding with the bending line (292). The machine further comprises an auxiliary structure (332) which measures the relative displacement of the punch (84) and the die (86) and is not influenced by the deformation of the tool-holder structure (288) induced by the bending force.

Description: Technical Field The present invention relates to a bending machine for the production of bent sheet-metal articles, of the kind defined in the preamble of claim 1. Background Art The invention has been developed to solve the problem of the bending of sheet-metal articles of complex shapes which are frequently used in machines such as photocopiers, facsimile machines and various electronic devices. These products are subject to rapid development and manufacturers therefore often change models from one year to another. Each new model is the product of a redesign, even as regards the various sheet-metal articles which it contains. These bent sheet-metal articles are therefore produced on a relatively small scale and thus do not justify complex and expensive tools and dies. A system of the above-mentioned kind, including a bending press for producing bent she-et-metal articles, is known from document US-A-4 991 422 and departs radically from previously existing bending systems which use bending presses with fixed frameworks and linear, V-sectioned punches and dies which are movable vertically towards and away from each other. The system described in US-A-4 991 422 provides for a piece which is to be bent to be supported by a manipulator so that a region of the piece which is to be bent lies in a vertical suspension plane. The bends are effected by means of an oscillating bending machine having two tools which can be disposed in any configuration relative to the piece to be bent. The piece is supported by the manipulator in a manner such that it can perform movements of limited extent with five degrees of freedom, excluding rotation about an axis perpendicular to the plane of the undeformed piece of sheet metal. Disclosure of the Invention The object of the present invention is further to develop a bending machine of the kind described in the aforementioned US-A-4 991 422. The object of the invention is achieved by means of a bending machine having the characteristics defined in the independent claim. Brief Description of the Drawings The present invention will now be described in detail with reference to the appended drawings, provided purely by way of example, in which: Figure 1 is a schematic, perspective view showing a system embodying the invention as a whole, Figures 2 to 9 show the bending machine indicated by the arrow II in Figure 1 and, more precisely, Figure 2 is a schematic, perspective view of the bending machine, Figures 3 and 4 are elevational and plan views of the bending machine, Figure 5 is a partial section taken on the arrow V-V of Figure 4, Figure 6 is a section taken on the line VI-VI of Figure 5, Figure 7 is a detail of the part indicated by the arrow VII in Figure 3, on an enlarged scale, Figures 8 and 9 are sections taken on the line VIII-VIII of Figure 7, showing the device for the rapid engagement of the tools. Best Mode for Carrying out the Invention A system for producing bent sheet-metal articles and a bending machine being part of the system will now be described with reference to the drawings. The system for producing sheet-metal articles With reference to Figure 1, a system for producing bent sheet-metal articles from blanked or laser-cut pieces of sheet metal of shapes corresponding to the development in a plane of the articles to be produced, is generally indicated 50. The system 50 comprises a station 52,for positioning the pieces of sheet metal, a measurement and storage station 54, a bending station 56, an output station 58 and a device 60 for the automatic replacement of the tools, with a respective tool store 62. The bending station 56 comprises a cartesian manipulator 64 including a vertically-movable device 66 carried by a carriage 68 movable along a beam 70 which in turn is movable along guides 72 of a portal structure 74. The movable device 66 of the manipulator 64 carries a suspension head 76 which will be described in detail below, for holding vertically, by means of a gripper, a piece of sheet-metal to be bent. The suspension head 76 of the manipulator 64 supports the piece in a manner such that it floats freely, so that the piece is free to perform movements of a limited extent during bending. In order to execute each bend, the manipulator 64, which is controlled by a conventional control unit 78, positions the piece in a position which is determined on the basis of a program established in dependence on the geometrical shape of the piece to be worked. The bending station 56 also comprises a bending machine 80 comprising a tool-holder structure 82 having a punch 84 and a die 86 which cooperate with each other. The tool-holder structure 82 is rotatable about an axis which passes through the bending line defined by the vertex of the V-shaped punch 84 and can also pivot about a horizontal axis perpendicular to the aforesaid axis of rotation. It will therefore be appreciated that the punch 84 and the die 86 can be disposed in any position relative to the piece to be bent. The rotary and pivoting movements of the tool-holder structure 82 are brought about by the control unit 78 on the basis of a predetermined program. It is important to underline that the precision of the positioning of the piece in space, like the precision of the positioning of the tools, is of decisive importance since, unlike conventional bending methods, there are neither mechanical abutments to define the position of the piece nor systems for measuring the position of the piece relative to the bending machine. The necessary precision in the positioning of the piece is achieved by virtue of a preliminary determination of the relative piece-manipulator position and of the precise control of the relative manipulator-bending machine positions, which is achieved by virtue of the operating precision of the manipulator 64 and of the bending machine 80. The operating principle upon which the bending system of Figure 1 is based thus consists of the positioning of a piece of sheet metal in a predetermined region in space with great precision and repeatability, and of the modification of the positions of the bending tools relative to the piece, with a corresponding degree of precision and repeatability, by a movement of the bending machine, so as to execute the bend in the desired region. For further clarification as regards the operating principle of the system according to the present invention, reference should be made to US-A-4 991 422. The main characteristic of the system according to Figure is its ability to work on extremely small batches (even a single piece) of pieces with different geometrical shapes, solely by means of the selection of a different working program, without carrying out tooling operations. A problem which had to be solved in order to achieve a high degree of flexibility of the system was that of devising a unit for loading the pieces which enabled shaped pieces of sheet metal of complex shapes and extremely variable dimensions to be stored and subsequently gripped by the suspension head 76 of the manipulator 64. With conventional grippers carried by the head of the manipulator, in addition to the difficulty of producing a universal gripper which can grip pieces of different geometrical shapes, there is the problem of the precise positioning of the piece relative to the gripper and hence relative to the locating system of the manipulator, that is, the problem of how to position the piece precisely on a loading device which, at the same time, can be adapted to pieces which differ greatly in shape and size. In the system according to Figure 1, these problems have been overcome by virtue of the fact that each piece is associated with its own gripper which is fitted on to a predetermined region of the undeformed piece of sheet metal. The gripper is fitted on to the piece of sheet metal in the positioning station 52. The pieces, with their respective grippers, are disposed in a store 90 to await transfer to the bending station 56. The store 90 can easily house pieces of different geometrical shapes without the need for any tooling, by virtue of the use of the gripper. In fact, the store 90 can accommodate a certain number of grippers which are inserted in a corresponding number of forks forming part of the store. The pieces of sheet metal, each gripped by its own gripper, are disposed vertically, suspended by the gripper itself, and thus have no direct connection with the store 90 which is completely independent of the shapes of the sheets. After each piece of sheet metal has been provided with its gripper, the piece is subjected to a measurement step carried out by means of a conventional feeler 88. The data detected by this measurement are processed and stored by the control unit 78 which establishes the link which exists between a locating system fixed relative to the piece and a locating system which is fixed relative to the gripper and, consequently, is fixed relative to the suspension head 76 of the manipulator 64. Small corrections can thus be made to the program controlling the manipulator 64 to compensate for errors in the positioning of the piece relative to the gripper. The piece may be measured when it is already connected to the suspension head 76 of the manipulator 64. In this case, the feeler 88 must be movable in order to enter and leave the working area. If the cycle for the working of the piece provides for the gripping region to be changed after some bends have been effected, a new measurement can be made after the piece has been gripped in the new position. Alternatively, and as shown in Figure 1, the measurement may be effected outside the working area, without affecting the time taken by the bending cycle, whilst the piece is supported by an auxiliary manipulator 89. The device 60 for replacing the tools of the bending machine 80 is constituted by a cartesian robot having a carriage 94 movable on a beam 96 which in turn is movable on the guides 72 of the portal structure 74. The bending machine Figure 2 to 9 show a bending machine embodying the present invention. With reference to Figures 2 to 4 in particular, the bending machine 80 comprises a fixed base 280 carrying a cradle 282 which is pivotable relative to the fixed base 280 about a horizontal axis 284. The cradle 282 is rotated about the axis 284 by a numerically-controlled motor 286. A tool-holder structure 288 is rotatably mounted on the cradle 282 by means of a thrust bearing 290 (Figure 3), the axis of rotation 292 of which coincides with the bending line defined by the vertex of the V-shaped punch 84. The tool-holder structure 288 is rotated about the bending line 292 by a numerically-controlled motor 294. The rotations of the tool-holder structure 288 about the axes 292 and 284 enable the punch-die unit to be placed in any position relative to the piece to be bent. Moreover, during the execution of each bend, the punch-die unit moves under the control of a predetermined program, following the natural movement of the flange of the piece due to the bending action. For a detailed description of the operation principle of the bending machine 80, reference should be made to the US-A-4 991 422 already mentioned above. With reference now to Figures 5 and 6, the tool-holder structure 288 comprises a strong, hollow C-shaped section 296 to the ends of which two pivoting supports 300, 302 (also visible in Figure 2) are articulated. The two supports 300, 302 are articulated to the C-shaped section 296 about axes 301, 303 perpendicular to the bending plane which is defined as the plane passing through the bending line 292 and through the direction of the relative movement of the tools of the bending machine, which is indicated by the double arrow 304 in Figure 5. The pivoting support 300 is intended to house the punch 84 and has a portion 306 having means which will be described in detail below for the rapid attachment of the punch. The pivoting support 302, on the other hand, has guides 308 (visible in Figure 6), along which a slide 310, movable along the axis indicated by the arrow 304, can slide. The slide 310 has a portion 312 which is similar to the portion 306 of the pivoting support 300, and has means for the rapid attachment of the die 86. The travel of the slide 310 relative to the pivoting support 302 is brought about by an actuator 314 carried by the pivoting support 302 and having two numerically-controlled electric motors, of which one brings about an approach travel of the slide 310 which is carried out at high speed and with low thrust, and the second brings about the bending stroke which is carried out at low speed and with high thrust (of the order of 7-8 t). The actuator 314 is described in detail in international patent application No. WO92/12362. As can be seen in Figure 5, each pivoting support 300, 302 is associated with a locating device 316 which can exert a resilient force on the respective pivoting support 300, 302, tending to keep the support in a predetermined position relative to the C-shaped section 296. Each locating device 316 comprises a rod 318 which is fixed to the respective pivoting support 300, 302 and extends with clearance through a hole in a step 320 fixed to the C-shaped section 296. Screwed onto the rod 318 is a pair of nuts 322 the positions of which are adjustable along the axis of the rod 318, and which define a stop surface cooperating with the fixed stop 320. The nuts 322 are urged into abutment against the respective stop 320 by the force produced by a helical compression spring 324 coaxial with the rod 318. It will be appreciated that the locating devices 316 allow the pivoting supports 300 and 302 to pivot solely in the senses indicated by the arrows 326 and 328 in Figure 5, pivoting in the opposite senses being prevented by the contact between the nuts 322 and the respective steps 320. The purpose of the arrangement described above is to ensure that the deformation of the C-shaped section 296 brought about by the bending load does not compromise the precision of the bend. In fact, the C-shaped section 296 tends to open out under the effect of the bending stress, deforming resiliently in the senses indicated by the arrows 330 in Figure 5. The same bending stress acting on the pivoting supports 300, 302, however, ensures that they remain in their original positions, so that the vertices of the punch and of the die remain constantly parallel to each other and to the theoretical bending line 292. An auxiliary measurement structure, indicated 332, disposed within the C-shaped section 296, has an arcuate profile with a tapered cross-section. A first end 334 of the measurement structure is fixed rigidly to the pivoting support 300 and a second end 336 is connected, by means of a spherical coupling 338, to an optical position-measuring instrument 340 which is slidable on a guide 342 carried by the pivoting support 302. The measuring instrument 340 faces an optical mark 342 fixed to the slide 310. Naturally, the positions of the measuring instrument 340 and of the optical mark 342 could be reversed with the mark connected to the auxiliary structure and the reader instrument connected to the slide 310. This arrangement enables the actual relative travel of the two bending tools to be measured regardless of the magnitudes of the deformations of the C-shaped section 296 brought about by the bending load. The measurements supplied by the instrument 340 are used to control the numerically-controlled motors of the actuator 314 and of the bending machine 80 which, as seen above, follow the movement of the flange of the piece. As has been seen, the deformations of the C-shaped section 296 affect neither the precision of the bend (by virtue of the pivotable mounting of the bending tools on the C-shaped section 296) nor the correct measurement of the relative spacing of the bending tools, by virtue of the measurement structure 332 which is independent of the C-shaped section 296. The C-shaped section 296 can consequently be of a size such that it is quite light, which is extremely advantageous, given that the tool-holder structure 288 is moved with rapid accelerations. The device for the rapid engagement of the bending tools on the tool-holder structure 288 will now be described with reference to Figures 7, 8 and 9. Only the device for rapid engagement between the die and the slide 310 will be described since the rapid engagement device for the punch is identical thereto, with the sole difference that the engagement device is disposed in the pivoting support 300 instead of in the body of the slide 310. With reference to Figures 8 and 9, which are sections taken on the line VIII-VIII of Figure 7, on an enlarged scale, a piston, indicated 344, is movable in a chamber 346 in which two regions 348 and 350 for supply with pressurized fluid are defined and are supplied in order to bring about the release and the engagement of the die 86, respectively. An engagement tooth 352 having a wedge-shaped surface 354 is fixed rigidly to the piston 344. The slide 310 has a plate 356 with flat bearing surfaces 358 against which corresponding surfaces 360 of the die 86 bear. A hole with a locating surface 372 is formed in the plate 356. The die 86 has a shank 362 having a locating surface 364 and a recess 366 with an inclined surface 368 for cooperating with the wedge-shaped surface 354 of the engagement tooth 352. A helical compression spring 370 interposed between the piston 344 and an internal end wall of the cavity 346 urges the piston 344 towards the engagement position shown in Figure 9. Starting from the configuration of Figure 8, in order to engage the die 86, pressurized fluid is sent to the supply region 348 so as to move the piston 344 against the action of the spring 370. The displacement of the engagement tooth 352 creates a space for the insertion of the shank 362 in the hole in the plate 356. The supply of fluid to the region 348 is then cut off but the region 350 is supplied, thus generating a force which is added to that generated by the spring 370, causing the piston 344 to move in the direction indicated by the arrow 374 in Figure 9. The purpose of the spring 370 is to ensure that the tool 86 remains connected to the portion 312 even if the supply of pressurized fluid to the region 350 should accidentally fail. The inclined surfaces 368 and 354 generate an oblique engagement force having a component parallel to the bending plane which keeps the flat surfaces 360 of the die 86 in contact with the flat surfaces 358 of the plate 356. The engagement force also has a component perpendicular to the bending plane which keeps the locating surface 364 in contact with the corresponding locating surface 372 of the plate 356. This enables precise and highly repeatable positioning of the bending tools relative to the slide 310 and relative to the pivoting support 300.

Claims: A bending machine, comprising: a fixed base (280), a cradle (282) mounted on the base (280) for pivoting about a horizontal pivot axis (284), a tool-holder structure (288) carrying a punch (84) and a die (86) which cooperate with each other and define a bending line (292), the tool-holder structure (288) being rotatable relative to the cradle (282) about an axis of rotation perpendicular to the horizontal pivot axis (284) and coinciding with the bending line (292), characterized in that it comprises an auxiliary structure (332) which measures the relative displacement of the punch (84) and the die (86) and is not influenced by the deformation of the tool-holder structure (288) induced by the bending force; in that the tool-holder structure (288) comprises a C-shaped section (296); in that the C-shaped section (296) is disposed in a bending plane which passes through the bending line (292) and through the axis (304) of the relative displacement of the tools (84, 86) and carries, articulated to its ends, first and second pivoting supports (300, 302), to which the bending tools (84, 86) are connected, the articulation axes (301, 303) of the pivoting supports being perpendicular to the plane; and in that the auxiliary measurement structure (332) has a first end (334) which is fixed to the first pivoting support (300) and a second end which is associated with a measurement device (338, 342) which can determine the relative displacement of a slidable slide (310) carried by the second pivotting support (302) and the second end (336) of the auxiliary measurement structure (332) along the axis of relative displacement of the tools (304). A machine according to Claim 1, characterized in that the first pivoting support (300) has means for the rapid attachment of a bending punch (84) having a vertex which, in the condition in which it is fitted on the first pivoting support (300), is aligned with the axis of rotation (292) of the tool-holder structure (288). A machine according to Claim 2, characterized in that a second pivoting support (302) carries a slidable slide (310) having means for the rapid attachment of a bending die (86). A machine according to Claim 1, characterized in that the pivoting supports (300, 302) are associated with respective locating devices (316) which can keep the supports (300, 302) in a position in which the vertices of the punch (84) and of the die (86) are parallel. A machine according to Claim 4, characterized in that each locating device (316) comprises two abutment surfaces (320, 322) of which one is fixed to a pivoting support (300, 302) and the other to the C-shaped section (296), and a resilient element (324) which tends to keep the abutment surfaces in contact with each other. A machine according to Claim 5, characterized in that each locating device (316) is disposed in a manner such that it allows the respective pivoting support (300, 302) to pivot only in the opposite sense to the sense of the rotation of the support caused by the resilient deformation of the C-shaped section (296) induced by the bending force. A machine according to Claim 2 or 3, characterized in that the means for rapid attachment of the punch or die (84, 86) comprises a tooth (352) for engaging a recess (366) formed in a shank (362) of the punch or die (84, 86), the tooth being movable in a direction perpendicular to the bending plane. A machine according to Claim 7, characterized in that the shank (362) of the punch or die has an inclined surface (368) for defining the recess (366), and the tooth (352) is formed with a wedge-shaped surface (354) for engaging the inclined surface (368).

Inventors: SARTORIO FRANCO, SARTORIO, FRANCO
Applicants: AMADA CO LTD, CREA SRL, AMADA COMPANY, LIMITED, CREA S.R.L.
Application year: 1994
Main classification: B21D5
IPC codes: B21D5, B21D43, B21D37, B21D11